When the then president of the European parliament, the Irish politician Pat Cox, arrived with a formal delegation in a small Czech village in order to discuss the complex implications of the Czech Republic joining the European Union in 1994, the first question quite unexpectedly posed by the local mayor was: "Do you know my good friend Russell Johnston?"

Perhaps the question should not have been so unexpected, for the Liberal Democrat politician Russell Johnston, who has died on the eve of his 76th birthday, spent his entire political career of nearly half a century in a passionate pursuit of European politics. He served as a member of the European assembly (predecessor of the directly elected European parliament), the Council of Europe and the Western European Union, and travelled constantly across the continent. He managed to do so while holding on to a difficult parliamentary seat - Inverness and then, from 1983, Inverness, Nairn and Lochaber - in the House of Commons for 33 years, before entering the House of Lords as a life peer in 1997: he had been knighted in 1985. He changed his name by deed poll to retain his full name as his title.

Johnston's majority at his last parliamentary election in 1992 was only 458 after three recounts, and, in an unprecedentedly close four-way contest, fewer than 2,000 votes separated the four main candidates. Although a popular man, he was nevertheless somewhat vulnerable to the charge "Russell's in Brussels" and correctly sensed that, even despite the fame of his name, he might have lost the seat in 1997 - when it was won by the Labour candidate.

He was regarded as a genial colleague at Westminster and - if he was around - was always happy to sink a glass (or several) more of his country's native spirit with like-minded friends. He was regarded with great affection by those who worked for him, both in the Commons and in the halls of European government, but it was also widely felt even by his own colleagues that he neglected his domestic interests in more ways than one, not least in his family life. One of his personal traits was to send postcards to all his friends from all over the world. Many must now have a large collection - but for his family it was not sufficient compensation for his absence.

He was bitterly disappointed not to win a seat in the directly elected European parliament - he was beaten twice by the Scottish Nationalist Winnie Ewing in 1979 and 1984 - but it did not diminish his enthusiasm for European affairs, and he was quite often switched on to crucial issues before other MPs. In May 1991, as the tanks were rolling into Ljubljana, the Slovenian capital, he had a question on the order paper to the then foreign secretary, Douglas Hurd, and was on his feet that day asking what the British government could do to assert his fears for the trouble that lay ahead in the probable breakup of the Yugoslav federation. He later travelled with his party leader, Paddy Ashdown, throughout the Balkans, and was present in 1992 when they were both filmed at the site of a Muslim prison camp where emaciated victims were discovered to have been subject to the brutality of Serbian warlords. The following year he spent a long night negotiating with the infamous Radovan Karadzic, unsuccessfully urging him to accept the negotiated peace plan for Bosnia.

His judgment was not always sound. In 1968 he incurred great criticism when he visited Greece during the colonels' regime in order to inspect the conditions of political prisoners - and to the fury of the liberal left, excused the military regime as "officers and gentlemen".

The strength of Russell-Johnston's absorption and interest in international affairs was in some ways puzzling in a man brought up on the Isle of Skye, but he believed in and spoke out for Scottish home rule and European union long before either became politically fashionable. He introduced a parliamentary bill seeking Scottish home rule in 1966, two years after he first arrived at Westminster, suitably attired in a kilt, and he never hesitated to express his opinion on both subjects, however controversial his views might have seemed at the time.

He achieved high office and great respect in the Liberal party - from 1989 the Liberal Democrats - over many years. He came into the Commons in the 1964 general election, a year before David Steel (who won a byelection in 1965) and their relationship was not without its political strains. Johnston declared himself a candidate for the party leadership in succession to Jo Grimond in 1976, and although he dropped out of the contest, in favour of John Pardoe, this did little to help their relationship. Steel had little choice but to name Johnston as Scottish spokesman when he became Liberal leader, recognising the authority Johnston held in the party in Scotland, where he was leader of the Scottish Liberals, a post he held from 1974 to 1988. He went on to play an important part in the Lib-Lab pact that kept James Callaghan's Labour government in office until 1979, leading the Liberal side on the negotiations with the late John Smith on the crucial topic of devolution, which proved fatal to that administration.

Johnston was also deputy leader of the Social and Liberal Democrats for four years after the merger of the two parties in 1988 - which he helped promote - and was then president of the Scottish Liberal Democrats for six years until 1994. He had attempted to push through an alliance between the Liberals and the Social Democrats once before, in 1983, arguing that the alternative was a "kamikaze course to political impotence".

Johnston was born in Edinburgh, but was a man of the Highlands. He was raised on Skye as a bilingual Gaelic speaker, was an enthusiast for shinty (a Scottish variation of hurling ) and vice chief of the Camanachd Association, the sport's governing body. His father was a customs officer, and he went to Carbost public school and Portree secondary school on Skye before taking a degree at Edinburgh University and qualifying as a teacher. He refounded the Liberal Club at the university, became its president and established himself as a successful public orator, winning trophies for public speaking from the Scotsman newspaper in 1956 and 1957, and subsequently the much-coveted Observer Mace in 1961.

For his national service, he was commissioned into the Intelligence Corps in 1958, and afterwards he taught at Liberton secondary school near Edinburgh (1961-63). By this time, however, he had already attracted attention within the Liberal party, which he then joined as a research assistant before winning his parliamentary seat.

He died in the street in Paris during a three-week holiday at his favourite hotel there, a place he regarded as a second home. His family life had suffered greatly as a result of his passionate political obsessions and he had in consequence been estranged from his wife, Joan, for a decade, although they remained close. He was diagnosed earlier this year with cancer of the bone marrow, for which he was receiving chemotherapy. "Nothing is forever," he said when he resigned as an MP. "However good the act, the curtain must come down." He and Joan were married in 1967 and he is survived by her and their three sons, Graham, David and Andrew.

Brian Wilson writes: Russell Johnston was a quintessentially Highland figure who ultimately grew weary of the local political grind and dedicated himself to his enthusiasm for European integration. His election to the Commons in 1964 helped prompt a Liberal revival in a region which had a longstanding loyalty to the party dating back to land reform legislation of the 1880s, but had gradually fallen into Tory hands; by comparison with that party's grandees, Russell practised an active, constituency-based form of politics.

It came as a great shock to him when he failed to be elected for the Highlands and Islands Euro-seat, almost certainly because he would not undertake to give up his Westminster seat. This was the second major disappointment of his career; in 1976, he was denied the chance of standing against David Steel and John Pardoe for the Liberal leadership, decided for the first time by popular vote of the membership, among whom Russell was highly regarded. But he first needed nominations from fellow MPs, which rival candidates managed to block.

Russell was probably the most able articulator of a distinctive Liberal philosophy of his generation. His speeches to Scottish Liberal conferences were invariably tours de force, which so impressed the journalist Neal Ascherson that he collected them into a book. Latterly, Russell found his ideal niche through the Council of Europe rather than domestic policies, but he will also be remembered for epitomising the best of the Highland Liberal tradition.

· David Russell Russell-Johnston, Lord Russell-Johnston, of Minginish in Highland, politician, born July 28 1932; died July 27 2008